This invention relates to an antenna having a motorized positioner connected thereto, whereby with operation of the positioner, the antenna is caused to shift on its mounting. More particularly, and as described herein, the invention concerns a positioner for moving a dish which receives signals from orbiting satellites, whereby the dish and its feed horn may be moved from a position aimed at one satellite, to pick up or acquire another satellite. While the invention is described in connection with such positioning of a signal-receiving dish, it is appreciated that features of the invention may have other applicability.
A so-called TVRO (television receiving only) dish is employed to receive signals from orbiting satellites in geosynchronous orbit over the equator of the earth. These satellites are approximately 23,000 miles in outer space, and are in orbit, but appear to remain stationary because of the rotation of the earth. With a so-called polar mount for the dish, i.e., a mount whereby the dish may be swung about an axis aligned in azimuth and elevation with the rotational axis of the earth, the dish may be swung about this pivot axis to change the satellite to which the dish is directed.
So-called linear actuators have been employed to move a TVRO dish. These are relatively inexpensive, and because of the geometry involved in the installation of a linear actuator, any play or looseness in the parts of the actuator does not introduce significant problems with respect to accuracy of positioning and dish movement caused by external factors such as wind buffeting. A disadvantage of a linear actuator is that such can produce controlled movement of a dish over an arc which is limited to about 140.degree. , meaning that a linear actuator may not produce movement of a dish from horizon to horizon. A gear-drive type of actuator may be employed to move a dish from horizon to horizon, but because of the geometry involved in such a system, any play or looseness in the parts of the gear drive results in inconsistency in the accuracy of adjustment and renders the dish controlled thereby sensitive to displacement under the action of buffeting winds. To overcome this problem, gear-drive units may be manufactured with tightly meshed gears manufactured under close tolerances, but this type of unit generally requires a more powerful motor to produce adjusting movement, and with any wear occurring in the parts, looseness is introduced with attendant inaccuracy and instability.
In general terms, an object of this invention is to provide an improved power-operated antenna positioner, which may be utilized to move an antenna such as a dish from horizon to horizon, without looseness or play in the parts introducing the problems above described.
More specifically, an object of the invention is to provide such a positioner which utilizes a gear drive to position the antenna or dish, more specifically, a worm wheel and meshing worm gear, and a construction which eliminates undesirable looseness or play. Following the invention, mass produced worm wheels and worm gears may be employed in the gear drive, with sufficient clearance provided for smooth and quiet running of the gears and the motor driving the gears, any clearance in effect being taken up in such a manner as to eliminate play or slop and attendant problems heretofore encountered.
In a specific and preferred embodiment of the invention, a gear-drive unit is employed to produce adjustable movement in the dish or antenna, which includes a worm wheel secured to a shaft, the axis of the shaft providing the pivot axis for movement in the dish and the shaft being secured to bracket structures supporting the antenna. The shaft is turned or rotated through a worm gear and motor assembly, both supported on a rocker plate or rocker, which is pivotable about an axis extending transversely of the axis of the worm wheel shaft, in a direction causing the worm gear to move toward the worm wheel and into snug engagement with the worm wheel. The assembly is biased in this direction through biasing means, such as a spring interposed between the assembly and framework such as a casing which may be provided for enclosing the drive parts of the gear-drive unit. With the teeth of the worm wheel and the helical drive of the worm gear having a slight taper, and with the organization described, the gear and wheel are always in snug engagement without undue loading of the motor which powers the unit and without conditions producing wear in the parts. The gear drive of the unit is self-adjusting, with the elimination of slop or looseness, even after repeated cycling of the dish or antenna across the sky.